Actually kicking around a TL idea that might incorporate something like this as a "butterfly" (won't be the main gist of the TL).
Most of the serious Liberia movement was from Virginia Planters, i.e. Madison, Monroe, etc. Jefferson was mixed on the idea.
If you butterfly Gabriel's Rebellion perhaps you see an 1830s manumission policy in VA, perhaps passed only by promise of a greater Colonization effort. Still, there's no way logistically to ship "everyone" back, as those above have noted, but you could see some early efforts at it or at least token "appease the people" motions which could conceivably lead to a significantly larger African American population in Liberia. This creates interesting butterflies for West Africa, particularly if we see an influx of skilled tradesmen (VA slaves were very often trained in woodworking, carpentry, metallurgy, or even rifle-making!), literate or semi-literate "house slaves" and perhaps educated freemen as an admin base, and former revolutionary and 1812 soldiers.